The present invention relates to machines for the manufacture of filter rods of the type which are used for the production of filter plugs or filter rod sections in the making of filter-tipped cigarettes, cigars or cigarillos. More particularly, the invention relates to improvements in apparatus which are used in filter rod making machines to apply a liquid plasticizer to successive increments of a continuously moving tow of filamentary filter material.
A filter rod making machine normally comprises a feeding or advancing mechanism which draws a continuous tow of filamentary filter material from a bale and transports the tow lengthwise through an impregnating station where the filaments are contacted by particles of a liquid plasticizer or softening agent. Prior to entering the impregnating station, the tow is caused to pass through one or more so-called banding devices wherein the tow is converted into a layer so as to expose all or nearly all of its filaments during travel through the impregnating station. The thus impregnated layer is thereupon caused to pass through a gathering device (called horn) which converts the layer into a rod-like filler to be thereupon wrapped into a web of cigarette paper or other suitable wrapping material to complete the conversion of the tow into a continuous filter rod. The rod is thereupon severed at regular intervals to yield filter rod sections or plugs of unit length or multiple unit length. The tow normally consists of cellulose fibers, and the purpose of the plasticizer is to soften portions of the surface on each filament so that the thus softened portions adhere to each other and form an integral network of filaments.
A drawback of presently known impregnating apparatus in filter rod making machines is that they are incapable of insuring that each increment or unit length of the tow contains the same quantity of plasticizer. As a rule, a conventional impregnating apparatus simply sprays atomized plasticizer against one side of the travelling layer of fibrous filter material and employs a suction nozzle which collects and leads away the particles of plasticizer which failed to adhere to the filamentary material. During further processing of filamentary material downstream of the impregnating station, a portion of the plasticizer evaporates and the remainder of the plasticizer hardens. The hardening or setting is completed simultaneously with subdivision of the filter rod into sections of desired length. If the quantity of plasticizer varies from unit length to unit length of the rod-like filler of filamentary filter material, the hardness of corresponding filter plugs also varies from plug to plug. The processing of filter plugs of non-uniform hardness presents serious problems, especially since the machinery which receives and further transports and processes filter plugs which are furnished by the filter rod making machine is not adjustable to compensate for variations in the hardness of plugs which are thereupon united with sections of wrapped tobacco particles to form filter cigarettes, cigarillos or cigars. As a rule, a relatively soft filter plug or section is more difficult to manipulate and is more likely to undergo permanent deformation or to be destroyed during treatment in a filter cigarette making machine or the like. Excessive deformation of a single relatively soft filter plug can cause lengthy interruptions in the operation of an entire production line with attendant losses in output.